Allotropes are pure forms of the same elements that differ in structure. Carbon has two main allotropes: diamond and graphite. Diamond is a cubic crystal of tetrahedrally-bonded carbon atoms. Diamond has a density of 3.51 grams per cubic centimeter. Graphite consists of parallel sheets of carbon atoms, each sheet containing hexagonal arrays of carbon atoms. The density of graphite is 2.25 grams per cubic centimeter. (A third allotrope, amorphous carbon, has a density ranging from about 1.8 to 2.2 grams per cubic centimeter. A fourth allotrope of carbon, consisting of a graphite-like sheet of carbon atoms that wraps to itself to form a ball, tube or similar structure, is referred to generally as a fullerene, and specific forms are known as buckyballs, carbon nanotubes and the like.) Natural diamonds are formed deep in the earth crust, under conditions of high temperature and pressure, and exist in a metastable state. Thus, diamond will revert to graphite if subjected to high temperature at low pressure. This reversion rate is function of temperature, pressure and time. Thus at 1000 degrees Celsius (° C.), diamond will revert to graphite at a slow but measurable rate.
Natural diamonds are commonly found in Kimberlitic pipes (commonly referred to as blue earth) expelled from great depths in the earth's crust. These diamonds are found in the presence of various minerals that contain a variety of elements including magnesium (Mg), aluminum (Al), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), cobalt (Co), titanium (Ti), and silicon (Si). These diamonds often have carbon inclusions as well as trace impurities that impart color to an otherwise colorless crystal. For example, nitrogen gas (N2) colors yellow.
A variety of techniques have been developed for artificially depositing and/or synthesizing diamonds. One type of diamond synthesis technique uses a high temperature, high pressure (HTHP) process. An HTHP process is described in U.S. Pat. No. 3,906,082 (hereinafter, “Shulzhenko et al.”), titled “METHOD OF MAKING DIAMONDS SYNTHETICALLY”, issued Sep. 16, 1975, and incorporated herein by reference. Shulzhenko et al. describe a method of diamond synthesis, by which a reaction mixture is prepared comprising, taken in direct contact, a carbonaceous material and a combination of components selected from the group containing silver chloride, calcium carbonate, calcium oxide and from a group containing aluminium and boron. Then the reaction mixture is subjected to the action of a temperature of at least about 1,800° C. and a pressure of at least 85 kbar for a time required for forming a diamond.
Another HTHP process is described in U.S. Patent Application Publication 2006 288927 A1 (hereinafter “Chodelka et al.”), titled “SYSTEM AND HIGH PRESSURE, HIGH TEMPERATURE APPARATUS FOR PRODUCING SYNTHETIC DIAMONDS”, published Dec. 28, 2006, and incorporated herein by reference. Chodelka et al. disclose an apparatus for growing a synthetic diamond comprises a growth chamber, at least one manifold allowing access to the growth chamber, and a plurality of safety clamps positioned on opposite sides of the growth chamber; wherein the growth chamber and the plurality of safety clamps are comprised of a material having a tensile strength of about 120,000-200,000 psi, a yield strength of about 100,000-160,000 psi, an elongation of about 10-20%, an area reduction of about 40-50%, an impact strength of about 30-40 ft-lbs, and a hardness greater than 320 BHN.
U.S. Pat. No. 4,984,534 (hereinafter, “Ito et al.”), titled “METHOD FOR SYNTHESIS OF DIAMOND”, issued Jan. 15, 1991, describes another diamond synthesis technique, and is incorporated herein by reference. Ito et al. describe a method for synthesis of diamond which is characterized by contacting a gas obtained by excitation of carbon monoxide and hydrogen in such a ratio as carbon monoxide being at least 1 mole % per total of carbon monoxide and hydrogen with a substrate in the presence of a reducing metal, a method for synthesis of diamond which is characterized by contacting with a substrate a gas obtained by excitation of carbon dioxide and hydrogen mixed at such a ratio of carbon dioxide being 0.1-20 mol % per hydrogen, and a method for synthesis of diamond by depositing diamond on the surface of a substrate by introducing onto the surface of the substrate a plasma obtained from hydrogen and carbon source gas by irradiation of microwave in a plasma generator which is characterized in that progress of microwave oscillated from one microwave oscillator is divided and thus divided respective microwaves and led to a plurality of plasma generators. Also disclosed is a diamond synthesis apparatus which is characterized by comprising a microwave oscillator for oscillation of microwave, a branched waveguide for dividing the microwave oscillated from said microwave oscillator and a plurality of plasma generators which are connected with said branched waveguide and have a substrate for deposition of diamond, respectively.
Another diamond synthesis technique is described in U.S. Pat. No. 7,235,130 (hereinafter, “Mao et al.”), titled “APPARATUS AND METHOD FOR DIAMOND PRODUCTION”, issued Jun. 26, 2007, and incorporated herein by reference. Mao et al. describe an apparatus for producing diamond in a deposition chamber including a heat-sinking holder for holding a diamond and for making thermal contact with a side surface of the diamond adjacent to an edge of a growth surface of the diamond, a noncontact temperature measurement device positioned to measure temperature of the diamond across the growth surface of the diamond and a main process controller for receiving a temperature measurement from the noncontact temperature measurement device and controlling temperature of the growth surface such that all temperature gradients across the growth surface are less than 20° C. The method for producing diamond includes positioning diamond in a holder such that a thermal contact is made with a side surface of the diamond adjacent to an edge of a growth surface of the diamond, measuring temperature of the growth surface of the diamond to generate temperature measurements, controlling temperature of the growth surface based upon the temperature measurements, and growing single-crystal diamond by microwave plasma chemical vapor deposition on the growth surface, wherein a growth rate of the diamond is greater than one micrometer per hour.
Chemical vapor deposition (CVD) is another technique for synthesizing diamonds. A CVD process is described in U.S. Pat. No. 7,258,741 (hereinafter “Linares et al.”), titled “SYSTEM AND METHOD FOR PRODUCING SYNTHETIC DIAMOND”, issued Aug. 21, 2007, and incorporated herein by reference. Linares et al. disclose synthetic monocrystalline diamond compositions having one or more monocrystalline diamond layers formed by chemical vapor deposition, the layers including one or more layers having an increased concentration of one or more impurities (such as boron and/or isotopes of carbon), as compared to other layers or comparable layers without such impurities. Such compositions provide an improved combination of properties, including color, strength, velocity of sound, electrical conductivity, and control of defects. A related method for preparing such a composition is also described, as well as a system for use in performing such a method, and articles incorporating such a composition.
U.S. Pat. No. 3,142,539 (hereinafter “Brinkman et al. '539”), titled “METHOD FOR ARTIFICIAL SYNTHESIS OF DIAMONDS”, issued Jul. 28, 1964, describes another diamond synthesis technique and is incorporated herein by reference. Brinkman et al. describe contacting a seed diamond being maintained at a temperature of about 1273-2073° K (1000-1800° C.), with a flux of carbon atoms exceeding a critical minimum value. Brinkman et al. describe the critical minimum value for the temperature difference as creating a graphite-saturation-limit carbon concentration (XGL(T2c)) in their molten solvent in their graphite-dissolving station at a higher temperature T2c wherein that carbon concentration is twice the graphite-saturation-limit carbon concentration (XGL(T1)) at the diamond-deposition location and diamond-deposition temperature T1 such that XGL(T2c)=2XGL(T1). In one embodiment described by Brinkman et al. the carbon atoms are transported from the carbon source (where their carbon source, graphite, is dissolving into their molten medium (e.g., lead)) to the surface of the diamond seed by the circulating molten medium. In another embodiment described by Brinkman et al. the carbon atoms are transported from the source to the surface of the seed diamond via a vapor stream in a vacuum or an inert gas atmosphere. Brinkman et al. assert that satisfactory metals meeting the required criteria of melting and boiling points, and carbon solubility ranges, for use as the molten medium are, for example, copper, lead, aluminum, bismuth, gold, silver, antimony, tin, gallium, indium, and germanium. Brinkman et al. assert such metals may be used either separately or together, for instance copper-gold, silver-gold, and lead-tin alloys. Brinkman et al. further describe that the seed diamond(s) is/are positioned on a stand held by a wire, and that vertical movement of the wire changes the position of the stand in an orifice, thereby providing flow regulation of the circulating molten medium.
U.S. Pat. No. 5,015,528 (hereinafter, “Pinneo”), titled “FLUIDIZED BED DIAMOND PARTICLE GROWTH”, issued May 14, 1991, describes a fluidized-bed diamond-synthesis technique and is incorporated herein by reference. Pinneo describes a process for forming synthetic diamond by vapor deposition of a carbon gas source in the presence of atomic hydrogen on a substrate contained in a gas-driven fluidized bed. The patent describes that the diamond may be overcoated by vapor deposition of a non-diamond material.
U.S. Pat. No. 5,609,926, (hereinafter, “Prins”), titled “DIAMOND DOPING”, issued Mar. 11, 1997, describes a method for doping diamonds with relatively large atoms such as aluminium, phosphorus, arsenic and antimony, and is incorporated herein by reference. Prins describes a method of producing a doped diamond including the steps of implanting dopant atoms in the diamond at low temperature to create a damaged region of point defects in the form of vacancies and interstitial dopant atoms within the crystal lattice of the diamond and annealing the diamond to reduce lattice damage and cause dopant interstitial atoms to move into lattice positions, the dopant atoms having an atomic number of at least 13 and being capable of providing the diamond with an optical or electrical property when situated in a lattice position in the crystal lattice of the diamond and the implantation dose being selected to create less damage than would be created when carbon atoms are implanted to a density of 2.5×1018/cm3.
An article by R. Ainsley, Linda P. Hartlib, P.M Holroyd and G. Long, titled “The Solubility of Carbon in Sodium”, Journal of Nuclear Materials 52 (1974) 255-276 (hereinafter, “Ainsley et al.”), describes the solubility of carbon in sodium and is incorporated herein by reference. Prior-art FIG. 1D herein is based on Ainsley et al. Ainsley et al. describe that the solubility of carbon in sodium has been determined over the temperature range of about 490 to 832° C. and can be expressed by the relation log10S (wt PPM)=7.646−5970/T(K). The authors state that the carbon is present probably as the dicarbide ion, except if oxygen or nitrogen is added, when the amount of dissolved carbon is enhanced by the formation of carbonate and cyanide respectively. When the sodium is cooled below freezing, the dissolved carbon readily plates out or absorbs on to surfaces in a way which is not easily reversed.
U.S. Pat. No. 3,038,409 (hereinafter, “Edgerly et al.), titled “EDDY CURRENT MAGNETIC LIQUID METAL PUMP”, issued Jun. 12, 1962, describes an apparatus for pumping electrically conductive fluid, and is incorporated herein by reference.
U.S. Pat. No. 4,105,493 titled “Production of shaving foil” issued to Jean-Daniel Chauvy on Aug. 8, 1978, describes a steel-etching technique useful for making fine-holed metal screens, and is incorporated herein by reference.
What is needed is an improved diamond-deposition process and system. In particular, there is a need for a more efficient low-pressure, low-temperature diamond-deposition process.